I purchased a used 2012 Mazda 6 with the 2.5L engine 4 months ago.

After driving it a little while, my wife and I both noticed that if the car sits after driving it any length of time, it will be harder to start. Harder to start = I go to start the car and it turns over, but it seems to take a few more seconds that normal like it would first thing in the morning after sitting overnight.

For example: I crank the car up no problem in the morning and drive to work. The car sits 8 hours in the parking lot or if I go to lunch, it's been sitting at least 5-6 hours and it cranks up fine. But, if I go back out in a couple of hours to leave for home, start the car, it take 3-4 seconds of turning the engine before it tries to start. And if the engine does try to run, it might stall out. Now, my wife and I have both tried this and when the engine is at the point it wants to run, but begins to stall, we'll give it gas and it will go ahead and run.

I took it to get an oil change today and the mechanic showed the plugs had age. I authorized to put NGK plugs in and the car seemed to run a little better. After describing the problem the mechanic said to drive it a few days and see if that helps. The cars runs quieter and smoother with the new plugs, that's for sure.

So i go back out 3-4 hours later and it's still doing the same problem with the new plugs in.

I'm thinking there might be a fuel issue meaning some sort of evaporation or leakdown is going on. The three hour mark for this starting issue happening is pretty consistent.

Granted, I took auto mechanics in high school 25 years ago and know the basics, but am not schooled on all this new tech. So is there anything I can look for, check or tell my mechanic? Hopefully, it's a minor and inexpensive fix.

Again, the car runs fine, it's just the above isn't right and I'd like it to start consistently.

Thanks!

 

Could be fuel pressure leaking off, but you say if it sits all day or overnight there is no issue.

Could be a dodgy temperature sensor, seen it before.